Heat resistant sheathed insulated electrical conductors

Abstract

The leads to a heater for an electrothermal hydrazine monopropellant thruster comprise tungsten conductors wrapped with smaller diameter tungsten support wire and insulated with beads of alumina (Al 2 O 3 ). A transition section connects the leads to regular leads. An attaching support wire is attached to the heater at one end and to the transition section at the other end. The insulated conductors and attaching wire are wrapped together with nickel ribbon to form a sheath.

We claim: 
     
       1. An electrical lead arrangement for a heater, said lead arrangement comprising: lead conductors principally of tungsten wire wrapped with smaller diameter tungsten support wire, with the lead conductors extending from within said heater to within a transition connector, and with each lead conductor insulated individually with alumina beads for at least part of the lead arrangement between but not within the heater and the transition connector; the lead conductors being connected within the transition connector to other lead wires which extend therefrom, and within the heater to a heater wire;   support means parallel to the insulated lead conductors, said support means comprising a solid attaching wire of a material selected from the group consisting of tungsten and molybdenum, with a diameter greater than the inner diameter but smaller than the outer diameter of the alumina beads;   and an outer sheath of heat-resistant metal around the insulated conductors and the attaching wire, wherein between the heater and the transition connector the lead arrangement has an overall diameter of less than one fourth inch with some flexibility, while being protected from mechanical or heat damage;   wherein said attaching wire has one end which is outside of said sheath and attached to said heater, and another end which is outside of said sheath and attached to the transition connector.   
     
     
       2. A lead arrangement according to claim 1, wherein said metal for said sheath is nickel in the form of a ribbon wrapped helically. 
     
     
       3. A lead arrangement according to claim 2, wherein said heater includes an insulating body means and a metal case means enclosing the insulating body, with a first hole extending through the metal case means, and two smaller holes extending into the the insulating body means; and wherein said lead arrangement further includes an exit insulator with a portion within said first hole, and a portion extending outside of the heater, the exit insulator having two holes extending through both said portions and aligned with said holes in the insulating body;   wherein each lead conductor extends through one of the holes of the insulating body, then through one of the holes of the exit insulator, then through said alumina beads up to the transition connector; and wherein said sheath extends over said portion of the exit insulator outside of the heater.